The invention relates to an integrated voltage divider consisting of the series arrangement of a number of resistors operated from a biasing voltage, whose tapping points are capable of being connected through via switching connections by means of a selection circuit to the voltage output, with the selection circuit, the resistors and the switching connections all being materialized in the insulated-gate field-effect transistor technique.
One such integrated voltage divider has been disclosed in DE-OS No. 29 30 375, claim 1, FIGS. 3 and 8. As the switching connections in this voltage divider there are used series arrangements of transistors of one uniform conductivity type, but of a different control type, i.e., enhancement type as well as depletion type transistors. The depletion type transistors are therein arranged at those points of the semiconductor body where two conductor leads cross each other, i.e., they serve as so-called tunnels.
For the examples of embodiment shown in the aforementioned FIGS. 3 and 8, employing eight resistors and one three-bit selecting signal, there is applied to the respective voltage divider tapping points, the series arrangement of the switching sections of up to eight transistors so that either, as in the case of FIG. 3, there is still added to the voltage-dividing resistors the internal resistance of these series arrangements or else, as in the case of FIG. 8, the series resistance to be taken into consideration, increases from tapping point to tapping point. The internal resistance of the voltage divider as seen from the voltage output, is accordingly composed of the actual voltage-dividing resistances and of the equivalent resistances of the individual series arrangements. The voltage output, however, shall be in connection with the voltage divider tapping points in a low-ohmic as possible manner which, however, is very difficult to obtain with the aid of the conventional arrangements.
Here, the invention is supposed to provide a remedy which, in the way as characterized in the claims, solves the problem of designing an integrated voltage divider of such a type, in such a way that between each voltage divider tapping point and the voltage output there will occur, if possible, the same resistance value, and that the selection circuit can be operated with a low as possible quiescent current.
Owing to the separation of the switching function from the selecting function as is provided for according to the invention, which two functions are combined in the series arrangements of the conventional circuits, it is possible to solve the given problem. In the course of this, there results the further advantage that far lower requirements have to be placed on the accuracy of the resistance values of the voltage divider than in the case of voltage dividers operating on the R-2R principle. This property is substantially secured by the fact that the switching connections between the voltage divider tapping points and the voltage output are materialized each time only by a single switching section or, in cases where transmission gates are used, by two parallel-arranged transistor switching sections.